This invention relates to a back-flow check valve having a flat valve seat with a central passage and a plurality of openings which are radially spaced from the central passage, and with the back-flow valve also including a mushroom-shaped closing member having a stem which is held in the central passage and a head of soft elastic material which covers the radially-spaced openings.
Such valves are used to cut off under pressure lines, such as, for example, in an under pressure fluid amplifier used in a motor vehicle. The following demands, among others, are placed on such a back-flow check valve:
a switching time must be quite small; PA1 a seal must be assured; and PA1 flow noises must not be created, that is, when a medium being controlled is air whistling noises must not be emitted.
If a tough elastic material is used for a closing member, or only for a closing member's head, the seal suffers because the closing member fails to adequately conform to a valve seat and also whistling noises are created. Whistling noises are best prevented by using a soft elastic material for the closing member and the seal is, at least in the beginning, also good; however, the seal will be diminished, after a short time, because a continuous "under pressure" applied to an interior side of the closing member will partially suck the closing member through the openings, so that, after a longer period of use, small knobs are formed on the interior surface of the head of the closing member. Because of this, sealing problems are created, particularly if the sealing member axially rotates a small amount. Further, the shape of the head will be easily deformed so that an outer edge thereof will no longer lie against the valve seat with a uniform force about its perimeter.
A possible remedy can be had by forming the openings to have smaller diameters. However, particularly for injection-molded valve seats, there are rigid limitations in that a die in the extrusion tool for making the openings, because of stability, cannot be too thin.
It is an object of this invention to provide a back-flow check valve of this general type that provides a good seal, does not create whistling noises, allows at least a head of a closing member to be constructed of a soft elastic material while not allowing it to be deformed at holes in a valve seat by being sucked thereinto, and indeed without the openings being made to have very small diameters.